Method and apparatus for detecting muscle fatigue

ABSTRACT

A method of and an apparatus for estimating the degrees of the fatigue and pain of muscles and comparing subjects of different weights on the same basis by deriving the variation in the muscular strength such as the dorsal muscular strength, shoulder muscular strength, the grasping power, and the like as an electric signal and integrating the muscular output on one hand, providing an integrated value of the electromyogrammatic amplitude by processing the voltage induced from the muscle to be tested through an electromyogram amplitude and a waveform processor, and by digitally displaying the ratio between these integrated values after correcting the ratio with a weight/muscular strength coefficient.

This is a continuation application from application Ser. No. 448,992filed Nov. 17, 1982, now abandoned; based on International ApplicationNo: PCT/JP81/00059, filed Mar. 18, 1981.

TECHNICAL FIELD

The present invention relates to a method of and an apparatus fordetecting muscle fatigue or pain. In particular, the present inventionrelates to a method of digitally representing the ratio between theintegral or integrated value of the electromyogrammatic amplitude of themuscle being tested to the integrated value of the muscular outputrepresenting the variation in muscular strength corrected by theweight/muscular strength coefficient. The present invention relates alsoto an apparatus for displaying the muscular strength, the maximumdischarge amount (mV) of the muscle being tested and the ratio betweenthe integrals of the electromyogrammatic amplitude and the muscularstrength on a panel display by passing the muscular strength such asdorsal muscular strength, shoulder arm strength and grasping powerthrough a transducer for providing an electric signal, an amplifier foramplifying the electric signal, an electromyogram amplifier coupled withdetection electrodes for deriving an action potential from the part ofmuscle being tested, and a waveform processor for processing thewaveform.

BACKGROUND ART

In a conventional load electromyogram used for measurement of fatigue byan electromygram, the load often has a constant value. For example, anexperiment on arm bending utilizing an ergometer was an experiment onthe fatigue resulting from repeated movements of raising a weighted bodyto a definite position, and not an experiment about the muscularstrength and the electromyogram in the process of reaching the maximummuscular strength. It was also impossible to know whether or not thesubject is already tired or feels pain at the time of measurement and,if he is tired or feels pain, what its degree is.

The inventor reported a method of recording the discharge amount derivedfrom a muscle being tested and the muscular strength of the muscle beingtested as a muscular strength electromyogram on a recorder by passingthe discharge amount through an input means and further anelectromyogram amplifier on the one hand, and by passing the muscularstrength through a transducer to convert it into an electric signalwhich is supplied to an amplifier on the other hand, the muscularstrength and electromyogrammatic signals from these amplifiers beingsupplied to a recorder amplifier and then to the recorder ("IndustrialMedicine," Vol. 18, No. 4, 1976, pp. 383 to 390). It has been found fromthe muscular strength electromyogram obtained by this method that theamplitude of the electromyogram increases as the muscular strengthincreases and the discharge amount of the muscle at the time of fatigueis higher than that when not tired. It has also been found that when themuscle is dead tired, the discharge amount increases considerably inspite of reduced muscular strength. However, there is a problem to thismethod that the degrees of fatigue cannot be exactly comparednumerically.

Also the inventor has found it necessary to find the areas of muscularstrength electromyograms to obtain the ratio therebetween in order toexactly compare the degrees of fatigue of muscles based on the muscularstrength electromyograms and reported a method of measuring andcomparing the areas of electromyograms ("Industrial Medicine," Vol. 20,No. 2, 1978, pp. 94 to 104). According to this method, the areas ofelectromyograms can be found by forming the envelopes thereof as shownin FIG. 9. However, this method has the disadvantage that not only isthere a considerable error in drawing envelopes due to differences ofindividuals, but also it is a time consuming and troublesome work toobtain the envelopes.

To overcome these shortcomings it was necessary to find the ratiobetween the integrals of the muscular strength and the electromyogram todisplay it.

On the other hand, the muscular strength depends on the constitution orphysique of the individual. The extent of the constitution can berepresented by the body weight. Since a person of a lighter weight islower in the muscular strength than a person of a heavier weight, theratio between the integrated values of the electromyogrammatic amplitudeto muscular strength is smaller even though the integrated values of theelectromyogrammatic amplitudes are the same. This fact suggests that thenumerical values of subjects of different weights cannot be compared asthey are.

The present invention has overcome these difficulties.

DISCLOSURE OF THE INVENTION

The present invention is to derive the variation in the muscularstrength such as dorsal muscular strength, shoulder arm strength,grasping power, or the like through a transducer as an electric signaland, at the same time, to record the electromyogrammatic waveforminduced from the necessary part of the muscle to be tested, thevariation in the muscular strength and the electromyogrammatic waveformbeing processed for digital representation of the maximum muscularstrength and the maximum amplitude, respectively, and the ratio betweenthe integrated values of the electromyogrammatic amplitude to themuscular strength being corrected by the weight/muscular strengthcoefficient for digital representation thereof.

The present invention employs a dorsal muscular strength, shoulder armstrength, or grasping power meter and applies electrodes to the rightand left neck regions, an upper part of the trapezius muscle, thedeltoid muscle, an interscapular region or space, a lumbodorsal region,the pectoralis major muscle, the antebrachial muscle, etc. to induce andmeasure the myoelectric signals.

Since electric signals obtained from these parts cannot be displayeddigitally as they are, they are subjected to waveform processing and thesignal components of 10 Hz or less and 150 Hz or more which do notappear on an electromyogrammatic meter are removed by means of ahigh-pass filter and a low-pass filter and then the electric signals aretransformed by a full-wave rectifier circuit into waveforms so that theycan be easily supplied to a digital processor. Then, envelope signalsare formed from these waveforms and passed through a low-pass filterwhich passes 3 Hz or less to get rid of fine variations and finallysupplied to a display.

On the other hand, separately therefrom, a signal derived from themuscular strength through a transducer and an amplifier is supplied to aprocessing indicator through a delay circuit to be processed after beingdelayed by the time equal to the delay time resulting from the waveformprocessing.

While a person of less fatigue has a high muscular strength and a lowdischarge amount, a person of more fatigue or pain has a lower muscularstrength and a higher discharge amount. To know the degree of fatigue orpain it is necessary to find the ratio of the discharge amount to themuscular strength (AMS ratio). However, since the muscular strengthdepends on the constitution or physique, to make a comparison betweensubjects on the same basis it is necessary to effect a weightcorrection.

The increase in the muscular strength is not proportional to increasesin weight, but its ratio (weight/muscular strength coefficient) isproportional to the weight raised to the power of 2/3. Thus, the weightcorrection value is, when the reference weight is assumed to be 50 Kg,as follows:

    P=50×(W/50).sup.2/3

where

P=weight correction value

W=weight

The progressive tendency of this correction value is 50 for a weight of50 Kg, 56.5 for 60 Kg, 62.8 for 70 Kg, 68.4 for 80 Kg, 74.0 for 90 Kg,79.4 for 100 Kg, while 43.1 for 40 Kg, 35.6 for 30 Kg, and 27.1 for 20Kg.

When the weight correction is made with these values, the dischargeamount/muscular strength ratio is multiplied by P/50. The correctionfactor is ×1 for the weight of 50 Kg and ×79.4/50 (=1.59) for 100 Kg,for example. The above-mentioned reference weight is not necessarily 50Kg. It can be replaced by any numerical value.

Since the AMS ratio obtained by this method has been affected by aweight correction, the fatigue and pain of subjects of different weightscan be compared on the basis of the same criterion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the apparatus of the present invention,

FIG. 2 is a block diagram of a waveform processor,

FIG. 3 is a block diagram of a digital processor,

FIG. 4 is a weight correction circuit,

FIGS. 5 to 8 are embodiments of the present invention, and

FIG. 9 is a diagram showing the method of finding the areas ofelectromyogrammatic waveforms 3 and 4 in FIG. 5 by means of envelopes.

BEST MODE OF CARRYING OUT THE INVENTION

A preferred form of the present invention will be described withreference to the drawings, wherein FIG. 1 is a block diagram of a dorsalmuscular strength meter for the measurement of muscular strength. Anaction potential is picked up from the muscle to be tested by surfaceelectrodes 1 and 1' applied thereto and supplied through an input part 2to electromyogram amplifiers 3 and 3' for amplification. The muscularstrength of the muscle to be tested is separately transformed into anelectric signal through a transducer 4 and then supplied to an amplifier5. The muscular strength and electromyogram signals derived from thedevices 3, 3' and 5 are recorded on a penrecorder 7 as a muscularstrength diagram and electromyograms through a recorder amplifier 6.Separately therefrom, the electromyogram waveforms and the muscularstrength derived from the devices 3, 3' and 5 are supplied to a waveformprocessor 8 to facilitate supplying the maximum values of theelectromyogram waveforms and the muscular strength recorded on thepenrecorder to a digitally processing display 9 and, at the same time,to facilitate the supply of the ratio between the integrated values ofthe electromyogrammatic amplitude to the muscular strength to thedisplay 9.

FIG. 2 is a block diagram associated with this waveform processor. Thesignal I produced by the devices 3 and 3' is shaped into the waveform IIand III by removing therefrom a low signal component of 10 Hz or lessdue to the movement of the electrode and a signal component of 150 Hz ormore which is not recorded on a penrecorder as an electromyogram bymeans of a high-pass filter (10) and a low-pass filter (11),respectively. The electromyogram waveform shaped into the waveforms IIand III is transformed by a full-wave rectifier circuit 12 into thewaveform IV which is facilitated to be supplied to a digitallyprocessing display 9.

If the rectified electromyogrammatic waveform IV is directly supplied tothe processing display 9, merely an average value of the signal isrecorded which is of a different value from that visually observed on apenrecorder. Therefore, the rectified electromyogrammatic waveform IV isconverted into an envelope signal V thereof through a peak hold circuit13 which has a discharge time longer than the charging time. The signalV is further passed through a low-pass filter 14 which passes signals of3 Hz or less to get rid of fine variations and then supplied to theprocessing display 9.

Separately therefrom, a muscular strength signal picked up through thetransducer 4 and the amplifier 5 is delayed by a delay circuit 15 by thetime equal to the time delay due to the wave processing and thensupplied to the processing display 9.

FIG. 3 is a block diagram of the digitally processing display 9. A partof the signal which was waveform-processed by the low-pass filter 14 inFIG. 2 is counted by a counter circuit 20 after passing through afrequency modulator 19 and supplied to a divider 21. The rest of thesignal from the low-pass filter 14 passes through a maximum detectioncircuit 16 and enters an electromyogram maximum value indicator 17 wherethe maximum amplitude is indicated by a numerical value of three digits.

A part of the muscular strength signal from the delay circuit 15 enters,after passing through the muscular strength correction circuit 18 and afrequency modulator 19', a counter 20' where it is counted and thenenters the divider 21. The rest of the signal from the delay circuit 15passes through a maximum value detection circuit 16' and then enters amuscular strength maximum value indicator 17' where the maximum muscularstrength is indicated by a numerical value of three digits.

From the signals supplied from the counter circuit 20 and 20' a divider21 processes the ratio between the integrated values provided by thelow-pass filter 14 and the delay circuit 15. The processed ratio isindicated on an indicator 22 as a numerical value of three digits. Thus,in order to cause the start and the end of integration processing of themuscular strength and the electromyogram at the same time, an adjustmentis made such that the integration starts when the muscular strengthrises to a set level from the zero level and stops when the muscularstrength returns to the same set level.

The numerical values indicated on the muscular strength maximum valueindicator 17' and the electromyogram maximum value indicator 17 showunder what functional conditions of the body the ratio between theintegrated values indicated on the indicator 22 was obtained. Forexample, for the same ratio between the integrated values, the muscularstrength and the electromyogram of a subject of inexhaustible vitalityshow high numerical values, whereas those of a subject of reducedvitality show low numerical values. Consequently, while the numericalvalue of the ratio between the integrated values alone cannot enablejudgment of functional conditions of a subject, the indication of themaximum values of the muscular strength and the electromyogram enablesthe functional conditions of the body to be known.

FIG. 4 shows a muscular strength correction circuit 18 for correctingthe muscular strength with the body weight. A muscular strength signalderived from the delay circuit 15 is supplied to an attenuator A theoutput of which is supplied to an amplifier B. The adjusting point Ad ofa divider D is set at a point higher or lower than 50 the by theadjustment value P of the weight adjuster on the panel of FIGS. 6 to 8.Thus, the signal supplied from the delay circuit 15 is amplified 50/Ptimes and divided and indicated through the frequency modulator 19' andthe counter circuit 20'. The correction value P can also be setautomatically by inputting the weight of the subject.

Examples of experiments according to the present invention will bedescribed with reference to FIGS. 5 to 8. The electrodes employed weredish-shaped surface electrodes which were applied to the parts to betested at an interval of 50 mm. The calibration voltage was 40 mm/200 Kgfor the dorsal muscular strength and 10 mm/1 mV for the electromyogram,and the time constant was 0.01 sec.

FIG. 5 is a record of the result of measurement of the dorsal muscularstrength electromyogram of a 22-year-old male subject who feelsoppressed at the right interscapular region. Electrodes were applied tothe parts to be tested of the human body diagram on the left in FIG. 5to measure the dorsal muscular strength and at the same time to recordthe electromyogram induced from the muscle to be tested. The dorsalmuscular strength was recorded on channel 2, the myoelectric signalsfrom right and left interscapular regions were recorded on channels 3and 4, the myoelectric signals from right and left lumbodorsal muscleson channels 5 and 6, all these being, at the same time, supplied to adata recorder.

Studying FIG. 5 it can be seen that the maximum dorsal muscular strengthis 138 Kg. This can be understood also from the muscular strength scale.An actual measurement of the maximum height of the curve shows 27.5 mm.Therefore, it is 138 Kg also considering the above calibration voltage.Next, in order to calculate the maximum values of theelectromyogrammatic amplitudes, the space between the horizontal linesdrawn above and below the amplitudes were measured. They were 2.18,5.24, 1.68 and 1.87 mV for Channels 3, 4, 5 and 6, respectively, in viewof the above calibration voltage. These maximum values are all indicatedon the panels of FIGS. 6 to 8. That is, on the left display window ofthe panel there is digitally indicated the maximum dorsal muscularstrength of 138 Kg, and 2.18, 5.24, 1.68 and 1.87 mV are digitallydisplayed on the upper display window Channels 3, 4, 5 and 6,respectively.

The ratios between the integrated values of the electromyogrammaticamplitude to the muscular strength corrected by the weight/muscularcoefficient according to the present invention are displayed on thelower display windows of the panels of FIGS. 6 to 8. These are AMSratios when the measurement records of FIG. 5 are retrieved and thecorrection value P is set for the weights of 50 Kg, 25 Kg and 100 Kg,respectively.

FIG. 6 is the case of the weight: 50 Kg. The correction value was set at50.0. The lower display windows of the panel displayed 0.71, 1.55, 0.64and 0.62 on the channels 3, 4, 5 and 6, respectively.

FIG. 7 is the case of the weight: 25 Kg. The correction value was set at31.5. The lower display windows of the panel displayed 0.45, 0.97, 0.40and 0.39 on the channels 3, 4, 5 and 6, respectively.

FIG. 8 is the case of the weight: 100 Kg. The correction value was setat 79.4. The lower display windows of the panel displayed 1.13, 2.46,1.01 and 0.98 on the channels 3, 4, 5 and 6, respectively.

The following table is a comparison between the variation in the abovedisplayed values and the increase in the weight.

    ______________________________________                                        Weight                                                                              Correction                                                                              Maximum Mus- Channel                                          Kg    Value     cular Strength Kg                                                                          3    4    5    6                                 ______________________________________                                        25    31.5      138          0.45 0.97 0.40 0.39                              50    50.0      138          0.71 1.55 0.64 0.62                              100   79.4      138          1.13 2.46 1.01 0.98                              ______________________________________                                    

While the maximum amplitudes at the upper parts of the display panels ofFIGS. 6 to 8 the discharge amount 1.87 mV on the channel 6 is higherthan 1.68 mV on the channel 5, in the lower windows the channel 5indicates 1.01 and the channel 6 indicates 0.98. Thus, the indication ofthe channel 5 is higher than that of the channel 6. This is because thefrequency of the electromyogrammatic amplitude was 70 Hz for the channel5 in contrast to 50 Hz for the channel 6. For this reason the channel 5displayed a higher value in the integration ratio.

As described above, the inventor has done research and development for along time on the muscular strength electromyogram in order to measurethe fatigue and pain of muscles. As shown in FIG. 5 the fatigue and painof muscles are clearly numerically expressed. This numerical value isone supporting the appeal of the subject that he feels oppressed at theright interscapular region.

INDUSTRIAL FEASIBILITY

The present invention measures the fatigue and pain of muscles andexpresses them numerically which no one could have done before. Theresults can be displayed exactly and in very short time as describedabove. The method of the present invention is characterized in that notonly the results of the processing can be displayed exactly and in avery short time as described above, but also the ratio between theintegrated values of the electromyogrammatic amplitude to the muscularstrength is digitally displayed after being corrected by weight/muscularstrength coefficient so that the displayed values can be compared underthe same condition even if there is imbalance in the displayed valuesdue to the difference in the weight.

I claim:
 1. A method for detecting muscle fatigue comprising the stepsof:(a) transforming the muscular strength of a muscle of a subject beingexamined into an electric muscular strength signal; (b) adjusting themuscular strength signal by a weight-muscular strength coefficient toprovide an adjusted muscular strength signal; (c) detecting amyoelectric discharge from the muscle being examined to form anelectromyogrammatic signal; (d) respectively integrating saidelectromyogrammatic signal and said adjusted muscular strength signal;and (e) determining the ratio between the integrated electromyogrammaticsignal and the integrated adjusted muscular strength signal.
 2. A methodaccording to claim 1, wherein said weight-muscular strength coefficientis represented by the formula:

    P=W.sub.o ×(W/W.sub.o).sup.2/3

wherein W_(o) is a reference weight and W is the weight of said subject,and said muscular strength signal is adjusted by multiplication byP/W_(o).
 3. A method according to claim 1, wherein the step (e)comprises dividing said integrated electromyogrammatic signal by saidintegrated adjusted muscular strength signal to derive said ratio.
 4. Amethod according to claim 1, further comprising the step of displayingsaid ratio.
 5. A method according to claim 4, further comprising thestep of displaying a maximum value of said electromyogrammatic signal.6. A method according to claim 4, further comprising the step ofdisplaying a maximum value of said muscular strength signal.
 7. A methodaccording to claim 5, further comprising the step of displaying amaximum value of said muscular strength signal.
 8. A method according toclaim 1, wherein the step (d) comprises respectively integrating asignal envelope of said electromyogrammatic signal and said adjustedmuscular strength signal.
 9. A method according to claim 1, wherein thestep (d) comprises:(d1) detecting a signal envelope of saidelectromyogrammatic signal; (d2) frequency-modulating a carrier signalwith the detected envelope so that the instantaneous frequency of themodulated carrier signal varies as a function of the instantaneous valueof said envelope; (d3) counting the oscillations of said modulatedcarrier signal to provide a count value representative of the integratedelectromyogrammatic signal; (d4) frequency-modulating a second carriersignal with the adjusted muscular strength signal so that theinstantaneous frequency of the modulated second carrier signal varies asa function of the instantaneous value of said adjusted muscular strengthsignal; and (d5) counting the oscillations of said modulated secondcarrier signal to provide a count value representative of the integratedadjusted muscular strength signal.
 10. A method according to claim 9,wherein the step (e) comprises determining the ratio between the countvalue of step (d3) and the count value of step (d5) as a digital value,and displaying said digital value by a display of decimal numbers. 11.An apparatus for detecting muscle fatigue comprising:(a) means includinga transducer for transforming the muscular strength of a muscle of asubject being examined into an electric muscular strength signal; (b)means for adjusting the muscular strength signal by a weight-muscularstrength coefficient to provide an adjusted muscular strength signal;(c) means for detecting a myoelectric discharge from the muscle beingexamined to form an electromyogrammatic signal; (d) means forintegrating said adjusted muscular strength signal; (e) means forintegrating said electromyogrammatic signal; and (f) means fordetermining the ratio between the integrated electromyogrammatic signaland the integrated adjusted muscular strength signal.
 12. An appartus asclaimed in claim 11, wherein said means for adjusting provides saidadjusted muscular strength signal by multiplication of said muscularstrength signal by P/W_(o), where P is said weight-muscular strengthcoefficient and is represented by the formula:

    P=W.sub.o ×(W/W.sub.o).sup.2/3

wherein W_(o) is a reference weight and W is the weight of said subject.13. An apparatus according to claim 11, wherein said ratio determiningmeans comprises means for dividing said integrated electromyogrammaticsignal by said integrated adjusted muscular strength signal.
 14. Anapparatus according to claim 11, further comprising means for displayingsaid ratio.
 15. An apparatus according to claim 11, further comprisingmeans for displaying a maximum value of said electromyogrammatic signal.16. An apparatus according to claim 14, further comprising means fordisplaying a maximum value of said muscular strength signal.
 17. Anapparatus according to claim 11, wherein said means for integrating saidelectromyogrammatic signal includes means for detecting a signalenvelope of said electromyogrammatic signal and means for integratingthe detected envelope.
 18. An apparatus according to claim 17, whereinsaid means for integrating said detected envelope comprises a firstfrequency modulator for modulating a carrier signal with the detectedenvelope so that the instantaneous frequency of the modulated carriersignal varies as a function of the instantaneous value of said envelope,and a first counter for counting the oscillations of said modulatedcarrier signal to provide a count value representative of the integratedelectromyogrammatic signal; andwherein said means for integrating saidadjusted muscular strength signal comprises a second frequency modulatorfor modulating a second carrier signal with the adjusted muscularstrength signal so that the instantaneous frequency of the modulatedsecond carrier signal varies as a function of the instantaneous value ofsaid adjusted muscular strength signal; and a second counter forcounting the oscillations of said modulated second carrier signal toprovide a count value representative of the integrated adjusted muscularstrength signal.
 19. An apparatus according to claim 18, wherein saidratio determining means comprises means for determining the ratiobetween the count value of said first counter and the count value ofsaid second counter as a digital value, and displaying said digitalvalue by a display of decimal numbers.
 20. An apparatus according toclaim 18, wherein said means for detecting a myoelectric dischargecomprises:a pair of electrodes adapted to be placed on the muscle beingexamined to generate a raw electromyogrammatic (EMG) signal havingalternating amplitudes; filter means for filtering out components ofsaid raw EMG signal having a frequency greater than a first value andless than a second value to produce a filtered EMG signal; and rectifiermeans connected to said filter means for rectifying said filtered EMGsignal, and wherein said envelope detecting means is connected to saidrectifier means.
 21. A method for detecting muscle fatigue comprisingthe steps of:(a) transforming the muscular strength of a muscle of asubject being examined into an electric muscular strength signal; (b)detecting a myoelectric discharge from the muscle being examined to forman electromyogrammatic signal; (c) respectively integrating saidelectromyogrammatic signal and said muscular strength signal; and (d)determining the ratio between the integrated electromyogrammatic signaland the integrated muscular strength signal.
 22. A method according toclaim 21, wherein the step (c) comprises the steps of:(c1)frequency-modulating a carrier signal with said electromyogrammaticsignal so that the instantaneous frequency of the modulated carriersignal varies as a function of the instantaneous value of saidelectromyogrammatic signal; (c2) counting the oscillations of saidmodulated carrier signal to provide a first count value representativeof the integrated electromyogrammatic signal; (c3) frequency-modulatinga second carrier signal with said muscular strength signal so that theinstantaneous frequency of the modulated second carrier signal varies asa function of the instantaneous value of said muscular strength signal;and (c4) counting the oscillations of said modulated second carriersignal to provide a second count value representative of the integratedmuscular strength signal; wherein the step (d) comprises dividing saidfirst count value by said second count value to derive said ratio.
 23. Amethod according to claim 22, further comprising the step of displayingsaid ratio as a digital value by decimal numbers.
 24. A method accordingto claim 23, further comprising the step of digitally displaying amaximum value of said electromyogrammatic signal by decimal numbers. 25.A method according to claim 23, further comprising the step of digitallydisplaying a maximum value of said muscular strength signal by decimalnumbers.
 26. A method according to claim 24, further comprising the stepof digitally displaying a maximum value of said muscular strength signalby decimal numbers.
 27. An apparatus for detecting muscle fatiguecomprising:(a) means for transforming the muscular strength of a muscleof a subject being examined into an electric muscular strength signal;(b) means for detecting a myoelectric discharge from the muscle beingexamined to form an electromyogrammatic signal; (c) first integratormeans for integrating said electromyogrammatic signal; (d) secondintegrator means for integrating said muscular strength signal; and (e)means for determining the ratio between the integratedelectromyogrammatic signal and the integrated muscular strength signal.28. An apparatus according to claim 27, wherein said first integratormeans comprises a first frequency modulator for modulating the frequencyof a carrier signal with said electromyogrammatic signal so that theinstantaneous frequency of the modulated carrier signal varies as afunction of the instantaneous value of said electromyogrammatic signal,and a first counter for counting the oscillations of said modulatedcarrier signal to provide a first count value representative of theintegrated electromyogrammatic signal;wherein said second integratormeans comprises a second frequency modulator for modulating thefrequency of a second carrier signal with said muscular strength signalso that the instantaneous frequency of the modulated second carriersignal varies as a function of the instantaneous value of said muscularstrength signal, and a second counter for counting the oscillations ofsaid modulated second carrier signal to provide a second count valuerepresentative of the integrated muscular strength signal; and whereinsaid ratio determining means includes means for dividing said firstcount value by said second count value to derive said ratio.
 29. Anapparatus according to claim 28, further comprising means for displayingsaid ratio as a digital value in decimal numbers.
 30. An apparatusaccording to claim 29, further comprising:means for detecting a maximumamplitude of said electromyogrammatic signal and representing thedetected maximum amplitude as a digital value; and means for displayingsaid digital value by decimal numbers.
 31. An apparatus according toclaim 29, further comprising:means for detecting a maximum amplitude ofsaid muscular strength signal and representing the detected maximumamplitude as a digital value; and means for displaying said digitalvalue by decimal numbers.